The present invention relates generally to vacuum operated desoldering tools utilized for the purpose of solder removal. More particularly, the invention relates to a device of the type wherein a piston mechanism is mounted for reciprocal movement within a tubular body having a nozzle at one end thereof, with the piston mechanism operating to produce a suction effect through the nozzle to effect the solder removal operation.
Tools of the type to which the invention relates generally comprise a piston mechanism which includes a piston member mounted on the forward end of a piston rod for reciprocatory movement within the tubular body of the tool. Tension spring means within the tool operate to displace the piston member rearwardly through a suction stroke, the piston member being thus moved from a forward position thereof located adjacent the forward end of the tubular body. Interlocking means for holding the piston member in its forwardmost position against the force of the tension spring means are provided and operating means are also provided which release the interlocking means thereby bringing the piston member into its rearwardmost position.
A suction nozzle having a through-bore is secured in a readily detachable manner at the forward end of the tubular body and a cleansing needle which protrudes from the forward end of the piston rod and which will extend into the through-bore of the nozzle may also optionally be provided.
An example of such a tool, which will hereinafter be referred to as a tool "of the type specified" is described in greater detail in British Pat. No. 1,195,525 to one of the co-inventors.
The present invention is directed toward providing an improved tool of the type specified particularly with regard to the quality of the vacuum achieved.
In order to achieve an optimum vacuum, a satisfactory sealing effect must be maintained between the piston mechanism and the inner wall of the tubular body. Furthermore, a minimal "dead volume" between the forward or front face of the piston mechanism and the adjacent body must also be attained. The first exigency mentioned above is generally self evident. However, the second exigency relating to the requirement for a minimal "dead volume" may be better understood if it is considered that the greater the volume of remaining air which is captured forwardly of the piston mechanism when in its forwardmost position, the greater will be the dilution effects upon the vacuum which must be created when the piston member is moved rearwardly. Thus, with greater amounts of residual air, a lower suction effect will be achieved. The volume which is located between the forwardmost face of the piston mechanism when at its forwardmost position and the inner face of the front wall of the tubular body will hereinafter be referred to as "the forward chamber". Ideally, the volume of the forward chamber when the piston mechanism is moved to its forwardmost position should be reduced to zero.
Molten solder which is drawn into the apparatus solidifies quickly and forms solid flakes or the like which will collect in the forward chamber and which will eventually prevent the piston mechanism from being brought to its intended forwardmost position. As a result, a greater amount of residual air will be retained in the forward chamber and the detrimental effects caused thereby will include the circumstance that the interlocking means will not longer operate dependably upon the piston rod of the piston mechanism. The reason for this is that the piston rod must be provided with engaging means for the interlocking means at a rearward location opposite the engagement means when the piston rod is in its forwardmost position. Because the accumulated solidified solder prevents the piston member from moving to its intended forwardmost position, the piston rod, which in accordance with prior art structures has conventionally been solidly attached or fixed to the piston member, is prevented from occupying its intended position relative to the interlocking means which thus can no longer act reliably.
It has been proposed in the prior art, e.g. British Pat. No. 1,215,548, to construct the piston member in the form of a long cylindrical plunger having arranged at its forward end a resilient sealing disk, with a stiff compression disk being formed forwardly thereof. The compression disk is coupled by means of an auxiliary rod to a conventional tension spring means of the apparatus so that when the plunger occupies its forwardmost position and the tension spring means is fully stretched, the resilient sealing disk will be axially compressed between the compression disk and the front face of the plunger with greater force than would otherwise be the case. Thus, an improved sealing effect is achieved as a result of the greater radial expansion of the compression disk which does not change its position relative to the plunger on the front face thereof where the resilient sealing disk fits at all instances.
The present invention is directed toward providing a tool of the type specified which will generally exhibit enhanced operating characteristics.